According to a report in Sunday’s New York Times, the Golden State contains two-thirds of the U.S.’s shale oil reserves, prompting a land rush to lock up leases for exploratory drilling.

That, as The Times notes, will tee up a monumental battle between California’s well-funded and politically powerful environmental groups and the oil and natural gas industries.

Thus it was particularly timely that Environmental Defense Fund president Fred Krupp, who runs one of the nation’s largest green groups, and Rhonda Zygocki, an executive at Chevron, one of the country’s biggest oil companies, appeared at the Commonwealth Club in San Francisco this week to debate “natural gas and the transition to a clean, low-carbon energy future.”

“We are undergoing a fundamental shift in our energy landscape that has the potential to keep energy affordable, to keep economic growth going and address our greenhouse gas emissions for years to come,” said Zygocki, Chevron’s vice president of policy and planning. “Shale was more of a nuisance than it was a gem for many years. But America is blessed with this rock.”

“As the cleanest burning fossil fuel, natural gas in combination with the progress we’re making in renewables and efficiency goes us the greatest potential than we’ve had before for more cost effective ways reduce greenhouse gases,” she added.

Many environmental groups, of course, see the shale gas boom unleashed by hydrofracking and horizontal drilling technologies as more a curse than a blessing, producing contaminated water supplies and air pollution while scaring local landscapes.

Krupp, whose organization is known for its partnerships with corporations like Walmart to advance its environmental goals, takes a more nuanced view.

“There’s no question that shale gas represents a big economic opportunity for this country and has created a lot of jobs,” he said, noting that replacing coal with cleaner natural gas can help in the transition to a renewable energy economy.

But that will only happen, Krupp said, if “we get the rules right” to prevent water and air pollution as well as contain fugitive emissions of methane, a byproduct of fracking and a potent greenhouse gas.

“Even a small amount of methane leaking accelerates global warming tremendously, especially within the next 20 years when we most need help in keeping the temperature rise down,” he said.

Lastly, Krupp said, it’s important that the nation’s utilities don’t lock in natural gas fired power plants for future electricity production at the expense of solar, wind, geothermal and other sources of renewable energy.

“At this pivotal moment we need to do all we can to accelerate truly clean energy,” he said. “If all that happens then [shale gas] could end up being not only a good thing for our country economically but environmentally.”

But it won’t be easy.

“There’s so many operators that even if the best 40 are doing everything perfectly there’s still another couple of thousand because it’s such a fragmented operation,” he said, adding that the jury was out on whether the states and federal government would adequately regulate the industry.

When I talked to Krupp a day after the panel he said one of the big challenges was just measuring methane emissions from fracking and determining the break-even point where any fugitive emissions would not exceed the carbon savings from replacing coal.

“For the last few years there have been all these studies come out about what are the emissions rates for all parts of natural gas production but none of them were based on going out and actually measuring the emissions,” he said.

EDF has joined a group of industry players and academics that have ventured into the field to measure actual methane emissions through the entire lifecycle of shale gas production and transport. The first results will be available for peer review in the coming weeks.

“Over the next year, instead of this data free discussion of this important issue, we should be moving to having a data rich discussion,” said Krupp. “We’ll get a better understanding where there are fugitive emissions escaping and where can we capture them and put them to work.”